With recent spread of a spout pouch, which is a packaging bag (pouch) to which a spout is attached, the spout pouch has been filled with various contents. Among the various contents filling such a spout pouch, for example, soy sauce, edible oil, liquor or the like is preferably prevented from being exposed to oxygen in the air in order to avoid deterioration due to oxidation. Accordingly, for the above contents, a spout pouch having a check valve mechanism has been demanded because it does not suck the outside air just after pouring out the contents.
Various containers with the check valve have been conventionally developed. In most of the containers with the check valve, contents are poured out by pressure applied to the container itself. That is, at the time of pouring out the contents, the container itself is pressed with a hand to increase the internal pressure of the container, so that the valve is opened by pressure of the contents and thereby the contents are poured out from the container. On the other hand, at the time of stopping the pouring out of the contents, the pressing on the container is stopped. Thereby, the container tends to return to its original shape, so that it generates depressurizing force that sucks the valve toward an inside of the container, and thus the valve is closed.
The mechanism described above functions well in the case where the container is made of a relatively hard material such as a blow bottle. However, in the case where the container is made of an extremely soft and thin laminated film or the like such as the spout pouch, even if the pressing on the container is stopped, the depressurizing force described above is hardly generated. Therefore, the valve is difficult to close, which causes a state that the pouring out the contents is not stopped well, and they drip from the port.
There is disclosed a check valve having a mechanism that closes a valve using restoring force of a coil spring, as a conventional check valve applicable to even the container such as a packaging bag (Patent Literature 1).
In the case of the check valve of this type, at the time of pouring out contents, the container is pressed and the valve is opened by pressure of the contents, like the check valve described above. On the other hand, at the time of stopping the pouring out of the contents, the pressing on the container is stopped. Thereby, the valve is closed by the restoring force of the coil spring.
Note that in Patent Literature 2, there is disclosed an infusion container in which a medical container and a flexible container are integrally formed, but the check valve is not described at all.